Analysis of Carbon Materials with Infrared Photoacoustic Spectroscopy.

Measurement of infrared spectroscopy has emerged as a significant challenge for carbon materials due to the sampling problem. To overcome this issue, in this work, we performed measurements of IR spectra for carbon materials including C60, C70, diamond powders, graphene, and carbon nanotubes (CNTs) using the photoacoustic spectroscopy (PAS) technique; for comparison, the vibrational patterns of these materials were also studied with a conventional transmission method, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, or Raman spectroscopy. We found that the IR photoacoustic spectroscopy (IR-PAS) scheme worked successfully for these carbon materials, offering advantages in sampling. Interestingly, the profiles of IR-PAS spectra for graphene and CNTs exhibit negative bands using carbon black as the reference; the negative spectral information may provide valuable knowledge about the storage energy, production, structure, defect, or impurity of graphene and CNTs. Thus, this approach may open a new avenue for analyzing carbon materials.

Enhanced structural integrity of Laser Powder Bed Fusion based AlSi10Mg parts by attaining defect free melt pool formations.

This research aims to fabricate an AlSi10Mg parts using Laser Powder Bed Fusion technique with enhanced structural integrity. The prime novelty of this research work is eliminating the balling and sparring effects, keyhole and cavity formation by attaining effective melt pool formation. Modelling of the Laser Powder Bed Fusion process parameters such as Laser power, scanning speed, layer thickness and hatch spacing is carried out through Complex Proportional Assessment technique to optimize the parts' surface attributes and to overcome the defects based on the output responses such as surface roughness on scanning and building side, hardness and porosity. The laser power of 350 W, layer thickness of 30 µm, scan speed of 1133 mm/s, and hatch spacing of 0.1 mm produces significantly desirable results to achieve maximum hardness and minimum surface roughness and holding the porosity of < 1%. The obtained optimal setting from this research improves the structural integrity of the printed AlSi10Mg parts.

Adapting the Time-Domain Synthetic Aperture Focusing Technique (T-SAFT) to Laser Ultrasonics for Imaging the Subsurface Defects.

Traditional ultrasonic testing uses a single probe or phased array probe to investigate and visualize defects by adapting certain imaging algorithms. The time-domain synthetic aperture focusing technique (T-SAFT) is an imaging algorithm that employs a single probe to scan along the test specimen in various positions, to generate inspection images with better resolution. Both the T-SAFT and phased array probes are contact methods with limited bandwidth. This work aims to combine the advantages of the T-SAFT and phased array in a noncontact way with the aid of laser ultrasonics. Here, a pulsed laser beam is employed to generate ultrasonic waves in both thermoelastic and ablation regimes, whereas the laser Doppler vibrometer is used to acquire the generated signals. These two lasers are focused on the test specimen and, to avoid the plasma and crater influence in the ablation regime, the transmission beam and reception beam are separated by 5 mm. By moving the test specimen with a step size of 0.5 mm, a 1D linear phased array (41 and 43 elements) with a pitch of 0.5 mm was synthesized, and three side-drilled holes (Ø 8 mm-thermoelastic regime, Ø 10 mm and Ø 2 mm-ablation regime) were introduced for inspection. The A-scan data obtained from these elements were processed via the T-SAFT algorithm to generate the inspection images in various grid sizes. The results showed that the defect reflections obtained in the ablation regime have better visibility than those from the thermoelastic regime. This is due to the high-amplitude signals obtained in the ablation regime, which pave the way for enhancing the pixel intensity of each grid. Moreover, the separation distance (5 mm) does not have any significant effect on the defect location during the reconstruction process.

Achieving effective interlayer bonding of PLA parts during the material extrusion process with enhanced mechanical properties.

The additive manufacturing technique of material extrusion has challenge of excessive process defects and not achieving the desired mechanical properties. The industry is trying to develop certification to better control variations in mechanical attributes. The current study is a progress towards understanding the evolution of processing defects and the correlation of mechanical behavior with the process parameters. Modeling of the 3D printing process parameters such as layer thickness, printing speed, and printing temperature is carried out through L27 orthogonal array using Taguchi approach. In addition, CRITIC embedded WASPAS is adopted to optimize the parts' mechanical attributes and overcome the defects. Flexural and tensile poly-lactic acid specimens are printed according to ASTM standards D790 and D638, respectively, and thoroughly analyzed based on the surface morphological analysis to characterize defects. The parametric significance analysis is carried out to explore process science where the layer thickness, print speed, and temperature significantly control the quality and strength of the parts. Mathematical optimization results based on composite desirability show that layer thickness of 0.1 mm, printing speed of 60 mm/s, and printing temperature of 200 °C produce significantly desirable results. The validation experiments yielded the maximum flexural strength of 78.52 MPa, the maximum ultimate tensile strength of 45.52 MPa, and maximum impact strength of 6.21 kJ/m2. It is established that multiple fused layers restricted the propagation of cracks with minimum thickness due to enhanced diffusion between the layers.

An investigation on osteoporosis based on guided wave propagation in multi-layered bone plates.

In this study, the multi-layer structure of bones has been used to simulate bone loss, and the guided waves were transmitted to the double-layer structured simulated bone plates, which are cortical bone and spongy bone. The soft tissue layer was simulated by water and the theoretical solution of the multilayer structure has been established. The guided waves were excited by the laser ultrasound technique and the Recursive Asymptotic Stiffness Matrix (RASM) was used to build a multilayer structure. Results show that, as the cortical bone is thinned, the dispersion relationship curve mode shifts toward high frequency and low phase velocity. Also, as the spongy bone density decreases, the dispersion relationship curve mode moves toward high frequency and high phase velocity. Further, it is found that, as the porosity rises, the mode of the dispersion relationship curve shifts to the direction of low frequency and low phase velocity. Through the addition of soft tissues and introduction of simultaneous changes in parameters, osteoporosis can be distinguished with high accuracy and hence this method can be applied to the detection of osteoporosis in the future.

Investigation on Microstructure, Nanohardness and Corrosion Response of Laser Cladded Colmonoy-6 Particles on 316L Steel Substrate.

316L steel is predominantly used in manufacturing the components of high-pressure boilers, heat exchangers, aerospace engines, oil and gas refineries, etc. Its notable percentage of chromium offers resistance against corrosion and is mostly implemented in harsh environments. However, long-term exposure to these components in such environments can reduce their corrosion resistance property. Particularly at high temperatures, the oxide film formed on this type of steel reacts with the chloride, sulfides, sulfates, fluorides and forms intermetallic compounds which affect its resistance, followed by failures and losses. This work is focused on investigating the hardness, microstructure and corrosion resistance of the laser cladded Colmonoy-6 particles on the 316L steel substrate. The cladded specimens were dissected into cubic shapes and the microstructure present in the cladded region was effectively analyzed using the FESEM along with the corresponding EDS mapping. For evaluating the hardness of the cladded samples, the nanoindentation technique was performed using the TI980 TriboIndenter and the values were measured. The potentiodynamic polarization curves were plotted for both the substrate and clad samples at 0, 18, 42 and 70 h for revealing the corrosion resistance behavior. In addition, the EIS analysis was carried out to further confirm the resistance offered by the samples. The surface roughness morphology was evaluated after the corrosion process using the laser microscope, and the roughness values were measured and compared with the substrate samples. The result showed that the cladded samples experience greater hardness, lower values of surface roughness and provide better corrosion resistance when compared with substrate samples. This is due to the deposition of precipitates of chromium-rich carbide and borides that enhances the above properties and forms a stable passive film that resists corrosion during the corrosion process.

Numerical Simulation and Non-Destructive Characterization of Material Property and Defect Analysis of Cortical Bone Using Laser Ultrasound Techniques.

The application of bone quality assessment has received extensive attention, and a large number of researchers continue to invest in related research activities. To get closer to the real situation, this study intends to investigate the long bones of cattle. A quantitative laser ultrasound visualization (QLUV) system was used to measure the images transmitted by the guided waves on the long bones, and the internal defects of the long bones were detected using wave propagation behavior. Then, linear scanning was performed through a laser ultrasound technique (LUT) to measure the dispersion curve of the cortical bone, and the results were compared with finite element simulations. Further, LUT was used to measure the material properties of the cortical bone in all directions. Finally, the long bones were scanned by computerized tomography to analyze the pore direction and distribution. Further, the relationship between pore direction and material properties was studied. The results showed that the obtained wave propagation image was consistent with the time-domain waveform signal and the finite element analysis results. The experimental and simulation results of wave velocity showed an error of 0.26 to 1.56% compared with the literature. The plate-shaped cortical bone showed that the phase velocity of the guided wave is higher than the circumferential direction. The defect location was identified through wave propagation behavior using the QLUV system. The elastic constant of the cortical bone was measured, and it showed the same trend as the results obtained from the tensile test in the literature. Also, the pore distribution indicated that the cortical bone porosity has the same trend as elastic constants. The elastic constants along the longitudinal direction were greater than the transversal direction. This laser ultrasound technique has been developed with an aim of having a better resolution and also as a potential application in osteoporosis conditions.

Surface alloying of FeCoCrNiMn particles on Inconel-718 using plasma-transferred arc technique: microstructure and wear characteristics.

Inconel-718 (IN-718) is a commonly used nickel-based superalloy in various fields, such as gas turbine and power generation applications. However, the lower wear and oxidation resistance hinder their wide usage. In this work, FeCoCrNiMn particles were mechanically ball-milled and preplaced on the IN-718 substrate. Then, the preplaced FeCoCrNiMn particles were scanned by heat source using plasma-transferred arc (PTA) technique. The effect of PTA alloying on the phase changes, microstructure, nanohardness and wear resistance has been investigated. The result showed that the PTA region contained different phases, such as FCC, BCC and intermetallic. No cracks were observed in the PTA alloyed region. Moreover, the porous free structure was viewed in the alloyed region, which revealed that the PTA alloying process was effectively used to perform the alloying process. More hard phases, such as NiFe, CoMn, Cr9Mn25Ni21, MnNi, FeCo, FeMn and MnCo, were formed on the PTA-alloyed region. The obtained wear rate of the substrate specimen at 30 N applied load is 2.45 × 10-3 mm3 m-1 and 1.79 × 10-3 mm3 m-1 for the PTA specimen. Similarly, the wear rate of the substrate specimen at 50 N is 5.38 × 10-3 mm3 m-1 and for the PTA sample, it is 2.29 × 10-3 mm3 m-1. The PTA specimen showed lower CoF than the substrate specimen due to increased surface hardness and minimum deformation of asperities. The primary wear type was mildly abrasive, accompanied by slight oxidative wear. Oxygen reacted with the surface alloying elements and formed different oxides, such as CoO, Cr2O3, MnO2, Mn2O3, Mn3O4, FeO and Fe2O3. These dense oxidation films covered the working surface and enhanced the wear resistance. The worn-out PTA surface showed that the wear scar depths were shallow and lower than the substrate, and reduced the roughness.

Fabrication of Coaxial and Confocal Transducer Based on Sol-Gel Composite Material for Optical Resolution Photoacoustic Microscopy.

We have newly developed coaxial and confocal optical-resolution photoacoustic microscopy based on sol-gel composite materials. This transducer contains a concave-shaped piezoelectric layer with a focus depth of 5 mm and a hole with a diameter of 3 mm at the center to pass a laser beam into a phantom. Therefore, this system can directly detect an excited photoacoustic signal without prisms or acoustic lenses. We demonstrate the capability of the system through pulse-echo and photoacoustic imaging experiments. The center frequency of the fabricated transducer is approximately 7 MHz, and its relative bandwidth is 86%. An ex-vivo experiment is conducted, and photoacoustic signals are clearly obtained. As a result, 2- and 3-dimensional maximum amplitude projection images are reconstructed.

Synergistic effect of l-ascorbic acid and hyaluronic acid on the expressions of matrix metalloproteinase-3 and -9 in human chondrocytes.

Proinflammatory cytokines and reactive oxygen species (ROS) are known to be involved in the initiation and progression of osteoarthritis (OA). New evidence clarifying the correlation between ROS and inflammation has indicated that oxidative stress can up-regulate inflammatory cytokines. l-Ascorbic acid (AA), an antioxidant, has been shown to have anti-inflammatory effects and improve matrix deposition in chondrocytes. The purpose of this study was to examine the effects of hyaluronic acid (HA; 100 µg/mL) supplemented with AA (50 µg/mL) on human normal and interleukin-1 beta-stimulated (IL-1ß, 10 ng/mL) chondrocytes. HA, AA, and HA + AA treatment did not change cell morphology, viability, proliferation, and glycosaminoglycan production in normal chondrocytes. HA, AA, and HA + AA, by contrast, partially restored viability and morphology of hypertrophic chondrocytes, and HA and HA + AA further decreased the cytotoxicity of IL-1ß. Real-time PCR revealed that AA and HA + AA had no substantial effects on unstimulated chondrocytes, except for down-regulation of matrix metalloproteinase (MMP)-9 mRNA levels. For IL-1ß-stimulated chondrocytes, significant down-regulation of IL-1ß, tumor necrosis factor-alpha (TNF-α), MMP-3, and MMP-9 mRNA expression was found when cells were cultured in HA-supplemented media. Moreover, HA + AA supplementation further significantly decreased MMP-3 and MMP-9 mRNA expression. The protein production of MMP-3 was decreased, with a significant difference between the HA + AA group and HA group. The antioxidant capacity and superoxide dismutases activity were also partially restored in stimulated chondrocytes. HA supplemented with AA modulates MMPs expression and antioxidant fuction in chondrocytes. AA may enhance the anticatabolic effects of HA on OA chondrocytes. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1809-1817, 2018.

Characterization of wedge waves propagating along wedge tips with defects.

Wedge waves are guided acoustic waves propagating along the tip of a wedge with the energy tightly confined near the wedge. Anti-symmetric flexural (ASF) modes are wedge waves with their particle motion anti-symmetric with the apex mid-plane. This study investigates the behaviors of ASF modes propagation along wedge tips with perfect and imperfect rectangular defects. Numerical finite element simulations and experimental measurements using a laser ultrasound technique are employed to explore the behaviors of ASF modes interacting with defects. Complex reflections and transmissions involved with direct reflections and transmissions as well as the newly discovered mode conversions will be explored and quantified in numerical as well as experimental ways.

Vibration Measurement Method of a String in Transversal Motion by Using a PSD.

A position sensitive detector (PSD) is frequently used for the measurement of a one-dimensional position along a line or a two-dimensional position on a plane, but is more often used for measuring static or quasi-static positions. Along with its quick response when measuring short time-spans in the micro-second realm, a PSD is also capable of detecting the dynamic positions of moving objects. In this paper, theoretical modeling and experiments are conducted to explore the frequency characteristics of a vibrating string while moving transversely across a one-dimensional PSD. The theoretical predictions are supported by the experiments. When the string vibrates at its natural frequency while moving transversely, the PSD will detect two frequencies near this natural frequency; one frequency is higher than the natural frequency and the other is lower. Deviations in these two frequencies, which differ from the string's natural frequency, increase while the speed of motion increases.

The Use of Flexible Ultrasound Transducers for the Detection of Laser-Induced Guided Waves on Curved Surfaces at Elevated Temperatures.

In this study, a flexible ultrasonic transducer (FUT) was applied in a laser ultrasonic technique (LUT) for non-destructive characterization of metallic pipes at high temperatures of up to 176 °C. Compared with normal ultrasound transducers, a FUT is a piezoelectric film made of a PZT/PZT sol-gel composite which has advantages due to its high sensitivity, curved surface adaptability and high temperature durability. By operating a pulsed laser in B-scan mode along with the integration of FUT and LUT, a multi-mode dispersion spectrum of a stainless steel pipe at high temperature can be measured. In addition, dynamic wave propagation behaviors are experimentally visualized with two dimensional scanning. The images directly interpret the reflections from the interior defects and also can locate their positions. This hybrid technique shows great potential for non-destructive evaluation of structures with complex geometry, especially in high temperature environments.

Anti-symmetric flexural modes for the detection of humidity variation.

Antisymmetric flexural (ASF) modes are guided acoustic modes propagating along the apex line of a wedge with particle motion that is antisymmetric about the midplane bisecting the apex angle. This paper describes experimental observations in applying ASF modes for the detection of moisture variation. In our setup, the wedge tip is coated with a thin layer of hygroscopic film for the absorption of moisture, so the phase velocity of the ASF mode is influenced by the changing humidity of the surrounding air. Enhanced by the wedge tip geometry, mass-loading effects on the ASF velocity resulting from the absorption of humidity are pronounced in a low-frequency regime of 0.2 to 2.0 MHz. Numerical models based on finite element analysis are constructed to explain the humidity sensing mechanism.

Guided waves propagating in a bi-layer system consisting of a piezoelectric plate and a dielectric fluid layer.

This study employs a theoretical modeling and an experimental measurement for investigating the dispersion behavior of guided waves propagating in a bi-layer system consisting of a piezoelectric plate and a dielectric fluid layer. The theoretical model is based on a recursive asymptotic stiffness matrix method (RASM) with the fluid layer modeled as an equivalent elastic body. A laser ultrasound technique is used to measure the dispersion relations of the bi-layer system. Behaviors of mode couplings between guided modes propagating in the piezoelectric plate and those in fluid layer are characterized in the modeling and measurements. Dispersion behaviors of guided modes propagating in the bi-layer system are discussed for varying fluid thicknesses. For all of the investigated cases, the theoretical modeled dispersion spectra agree well with the measurements.

Characterization of mechanical and geometrical properties of a tube with axial and circumferential guided waves.

Guided waves propagating in cylindrical tubes are frequently applied for the characterization of material or geometrical properties of tubes. In a tube, guided waves can propagate in the axial direction and called axial guided waves, or in the circumferential direction called circumferential guided waves. Dispersion spectra for the axial and circumferential guided waves share some common behaviors and however exhibit some particular behaviors of their own. This study provides an investigation with theoretical modeling, experimental measurements, and a simplex-based inversion procedure to explore the similarity and difference between the axial guided waves and circumferential guided waves, aiming at providing useful information while axial and circumferential guided waves are applied in the area of material characterization. The sensitivity to the radius curvature for the circumferential guided waves dispersion spectra is a major point that makes circumferential guided waves different from axial guided waves. For the purpose of material characterization, both axial and circumferential guided waves are able to extract an elastic moduli and wall-thickness information from the dispersion spectra, however, radius information can only be extracted from the circumferential guided waves spectra.

A comparison of laser ultrasound measurements and finite-element simulations for the dispersion behavior of antisymmetric flexural modes propagating along wedge tips with coatings.

Antisymmetric flexural (ASF) modes are antisymmetric types of guided waves propagating along the tip of wedge-shaped waveguides. Acoustic sensors frequently rely on the detection of small mass changes that result from binding a coated layer coupled to the active sensor surface. While a layer is coated on one of the wedge's surfaces, another type of sensor can be potentially developed based on detecting the change of ASF velocity. This paper describes a study on the effects of ASF dispersion behavior for a wedge with a layer of coating using a combined numerical and experimental investigation. In this study, the frequency range is from 0.5 MHz to 10 MHz, and the effective wave propagation length along the wedge tip ranges from 3 mm to 13 mm. Brass wedge tips coated with aluminum layer are studied for the case of slow matrix with fast coating, while aluminum wedge tips with copper coatings are studied for the case of fast matrix/slow coating combination. Like surface acoustic waves propagating along a flat surface with a layer of coating, loaded and stiffened phenomena are observed for the ASF modes traveling along coated wedges. Moreover, the wedge tip geometry is found to have an effect in enhancing the loaded and stiffened phenomena. The numerical results show good agreement with experimental results.

Experimental and numerical investigations on the dispersion behaviors of wedge waves propagating along wedges with bilinear cross sections.

Wedge waves (WW) are guided acoustic waves propagating along the tip of a wedge, with energy tightly confined near the apex. This study is focused on exploring the dispersion behaviors of WW propagating along a bilinear wedge (BW). A BW is wedge with a cross section of two apex angles, compared with a linear wedge (LW) having a single apex angle. In the literature, many studies regarding to the dispersion behaviors of ASF modes are reported for LW, but not for BW. In this study, a combined experimental and numerical stidy is used to investigate the dispersion behavior of WW propagating in BW's. It is found out that WW in a BW is a result of mode coupling between the two WW's corresponding to simple wedges with the two apex angles of the BW.

A new optical method for the detection of in-plane motion of ultrasound propagating in metals.

This paper describes a laser optical technique for the detection of in-plane (IP) motion of ultrasonic waves propagating in solids. This interference-based laser optical technique includes a tiny square indentation with a width of about 30 microm on the sample surface and a relatively simple optical arrangement. The current technique is applied for the detection of in-plane motions of Lamb waves propagating in a thin brass plate. Measurement of S(0) mode dominated by in-plane motion in the low fd (frequency times thickness) regime is successfully demonstrated with the current technique. The newly proposed non-contact technique provides an alternative other than the heterodyne and Fabry-Perot techniques for the detection of IP motions with a relatively simple optical arrangement. This technique is not readily applicable to general NDE applications, where a position scan or an arbitrary selection of inspection location is needed. However, this technique can be useful in the areas such as fixed-position ultrasound monitoring or laboratory research activities involving optical detection of IP motion.

A study on the dispersions of piezoelectric plate with laser ultrasound measurement and theoretical modeling.

This research is focused in the measurement and modeling for the dispersion relations of Lamb waves propagating in LiNbO(3) and LiTaO(3) plates. A theoretical model based on a stiffness matrix method with recursion computation algorism is used to provide numerical calculations for the dispersion relations. Also, a dry, noncontact laser ultrasound technique is used to measured dispersion multi-mode dispersion relations. For all the experiments, the measured dispersion curves show good agreement with the theoretical calculation, indicating the reliabilities in the measurement and modeling.